Articles for high temperature service and related method

ABSTRACT

An article for high temperature service is presented. The article includes a substrate and a thermal barrier coating disposed on the substrate. The thermal barrier coating includes a plurality of aluminum-based particles dispersed in an inorganic binder, wherein the aluminum-based particles are substantially spaced apart from each other via the inorganic binder such that the thermal barrier coating is substantially electrically and thermally insulating. Method of making the article is also presented.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.15/891,241 filed Feb. 7, 2018, which claims the priority benefit ofApplication Ser. No. 62/529,165 filed Jul. 6, 2017, the entireties ofwhich are incorporated by reference herein.

BACKGROUND

The disclosure relates generally to coatings used in articles for hightemperature service. More particularly, the disclosure relates toarticles including thermal barrier coatings.

Thermal barrier coatings are typically used in articles that operate ator are exposed to high temperatures, e.g., gas turbine engines. Use ofthermal barrier coatings in the automotive industry has also been foundto yield a significant effect on the efficiency of engines. Thermalbarrier coatings typically allow for higher operating temperatures,thereby enabling higher fuel efficiencies.

The selection of thermal barrier coating materials is restricted byrequirements, such as, high melting point, no/minimal phasetransformation between room temperature and operation temperature, lowthermal conductivity, chemical inertness, thermal expansion match withthe underlying substrate, and good adherence to the underlyingsubstrate. Typically, ceramics (e.g., yttria stabilized zirconias,zirconates, pyrochlores and the like) have been employed successfully asthermal barrier coating materials. However, for applications such asautomotive applications, the ceramic materials may not be cost effectiveand may suffer from poor adherence with the underlying metallicsubstrates (e.g., aluminum-based substrates) because of poor chemicalcompatibility between the metallic substrate and the ceramic material.

Both aluminum and alumina-based coatings are known in the art, and areused, for example, as diffusion coatings for superalloy substrates or assacrificial galvanic corrosion resistant coatings for steel substrates.

Typically, cobalt- or nickel-based superalloys, used forhigh-temperature turbine engines applications, contain aluminum, whichis a key component for the precipitation-strengthening of the material.However, exposure to an oxidizing temperature for an extended period mayresult in aluminum depletion at the surface. Since loss of aluminum canbe detrimental to the integrity of the superalloy, techniques forcountering such a loss have been investigated. One method for increasingthe aluminum content of the superalloy substrate (i.e., in its surfaceregion) is sometimes referred to in the art as “aluminiding” or“aluminizing”. In such a process, aluminum is introduced into thesubstrate by applying an aluminum or alumina based coating (e.g., as aslurry including a binder) on the substrate and subjecting the coatingto diffusion heat treatment at temperatures greater than 870° C. Theelevated temperature causes the aluminum to melt and diffuse into theunderlying substrate to form various intermetallics, e.g., ametal-aluminide compound. For example, in the case of a nickel-basesuperalloy substrate, the aluminum diffuses and bonds with the nickel toform various nickel-aluminide alloys. The diffusion coatings based onmetal aluminides therefore require heat treatment using substantiallyhigh temperatures (greater than 870° C.). At such elevated temperatures,the binder components employed for deposition of the coatings aretypically volatilized and the final coating after the heat treatmentessentially consists of metal aluminides.

Corrosion-resistant coatings have been developed for high strengthsteels to prevent/minimize stress corrosion cracking. One of the commoncommercially-available coating employs water-based slurries containingan aluminum-based dispersion in an acidic solution, containing anionssuch as phosphates and chromates. Upon exposure to heat and curing,these slurries transform to an insoluble electrically conductivemetal/ceramic composite. These coating formulations are designed andprocessed such that the coatings are sacrificial as well as electricalconductive, thereby rendering a galvanic property to the substrate. Insome cases, where the substrate for the coating is ferrous metal, thealuminum powder in the coating, by way of electrochemical reactionswhich ensue in a salt-spray or other corrosive atmosphere, generallysacrifices itself to the end that there is little or no corrosion of theferrous metal substrate. It has further been established that thesacrificial property of the coating in providing the increased corrosionprotection is greatly enhanced by so processing the coating as to renderit electrically conductive. Usually, the aluminum filled coatings aremade sacrificial and galvanically active by either cold working(burnishing) the coating surface, or by heat treating. The goal is toproduce an electrically conductive aluminum coating that is sacrificial,i.e., will corrode and protect the adjacent base metal areas fromcorrosion. Therefore, the aluminum loading in these compositions ismaintained to be sufficiently high such that the coatings areelectrically conductive. Further, the coatings are designed such thatthe aluminum content in the coating reduces during use, therebyrendering the coating sacrificial.

However, the diffusion-based aluminide coatings or the sacrificial,galvanic coatings may not be effective for providing the desiredcharacteristics while functioning as a thermal barrier coating. Forexample, a sacrificial, galvanic coating may have a high thermalconductivity value because of the higher loading of aluminum in thecoating and may therefore not meet the thermal conductivity requirementsof a thermal barrier coating. Further, the diffusion-based aluminidecoatings or the sacrificial, galvanic coatings may not have the desiredcoefficient of thermal expansion match with the substrate, which maylead to potential spallation and failure of the coatings.

Thus, there is a need for improved coating compositions that canfunction as thermal barrier coatings. Further, there is a need forimproved methods for forming the thermal barrier coatings.

BRIEF DESCRIPTION

One embodiment of the disclosure is directed to an article including asubstrate and a thermal barrier coating disposed on the substrate. Thethermal barrier coating includes a plurality of aluminum-based particlesdispersed in a binder, wherein the aluminum-based particles aresubstantially spaced apart from each other via the binder such that thethermal barrier coating is substantially electrically and thermallyinsulating.

Another embodiment of the disclosure is directed to an article includingan automotive component. The automotive component includes a substrateand a thermal barrier coating disposed on the substrate. The thermalbarrier coating includes a plurality of aluminum-based particlesdispersed in a binder, wherein the plurality of aluminum-based particlesincludes a core-shell structure, wherein a core of the core-shellstructure includes aluminum metal and a shell of the core-shellstructure includes a complex of the binder and one or both of aluminumand alumina.

Another embodiment of the disclosure is directed to a method of forminga thermal barrier coating on a substrate. The method includes contactinga slurry including a plurality of aluminum-based particles and aninorganic binder with a surface of the substrate to form a slurrycoating. The method further includes heat-treating the slurry coatingunder conditions sufficient to cure the slurry coating and form thethermal barrier coating, wherein the aluminum-based particles aresubstantially spaced apart from each other via the binder in the thermalbarrier coating such that the thermal barrier coating is substantiallyelectrically and thermally insulating.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features, aspects, and advantages of the presentdisclosure will become better understood when the following detaileddescription is read with reference to the accompanying drawings, inwhich like characters represent like parts throughout the drawings,wherein:

FIG. 1 illustrates a schematic of an article, in accordance with anembodiment of the disclosure;

FIG. 2 illustrates a schematic of an article, in accordance with anembodiment of the disclosure;

FIG. 3 illustrates a schematic of an article, in accordance with anembodiment of the disclosure;

FIG. 4 illustrates a schematic of an article, in accordance with anembodiment of the disclosure;

FIG. 5 illustrates a schematic of an article, in accordance with anembodiment of the disclosure;

FIG. 6 illustrates a flow chart of a method of forming a thermal barriercoating, in accordance with an embodiment of the disclosure;

FIG. 7 illustrates a method of forming a thermal barrier coating, inaccordance with an embodiment of the disclosure; and

FIG. 8 illustrates an optical micrograph of the microstructure describedin the Examples.

DETAILED DESCRIPTION

Approximating language, as used herein throughout the specification andclaims, may be applied to modify any quantitative representation thatcould permissibly vary without resulting in a change in the basicfunction to which it is related. Accordingly, a value modified by a termor terms, such as “about”, and “substantially” is not to be limited tothe precise value specified. In some instances, the approximatinglanguage may correspond to the precision of an instrument for measuringthe value. Here and throughout the specification and claims, rangelimitations may be combined and/or interchanged, such ranges areidentified and include all the sub-ranges contained therein unlesscontext or language indicates otherwise.

In the following specification and the claims, the singular forms “a”,“an” and “the” include plural referents unless the context clearlydictates otherwise. As used herein, the term “or” is not meant to beexclusive and refers to at least one of the referenced components beingpresent and includes instances in which a combination of the referencedcomponents may be present, unless the context clearly dictatesotherwise.

As used herein, the terms “may” and “may be” indicate a possibility ofan occurrence within a set of circumstances; a possession of a specifiedproperty, characteristic or function; and/or qualify another verb byexpressing one or more of an ability, capability, or possibilityassociated with the qualified verb. Accordingly, usage of “may” and “maybe” indicates that a modified term is apparently appropriate, capable,or suitable for an indicated capacity, function, or usage, while takinginto account that in some circumstances, the modified term may sometimesnot be appropriate, capable, or suitable.

As used herein, the term “coating” refers to a material disposed on atleast a portion of an underlying surface in a continuous ordiscontinuous manner. Further, the term “coating” does not necessarilymean a uniform thickness of the disposed material, and the disposedmaterial may have a uniform or a variable thickness. The term “coating”may refer to a single layer of the coating material or may refer to aplurality of layers of the coating material. The coating material may bethe same or different in the plurality of layers.

As used herein, the term “disposed on” refers to layers or coatingsdisposed directly in contact with each other or indirectly by havingintervening layers there between, unless otherwise specificallyindicated. The term “disposing on” refers to a method of laying downmaterial in contact with an underlying or adjacent surface in acontinuous or discontinuous manner. The term “adjacent” as used hereinmeans that the two materials or coatings are disposed contiguously andare in direct contact with each other.

As used herein, the term “ceramic” refers to an oxide, carbide, nitride,etc., of a metal. As used herein, the term “substantially free” meansthe indicated compound, material, component, etc., is minimally presentor not present at all, e.g., at a level of about 0.5 weight percent (wt%) or less, more typically at a level of about 0.1 percent (wt %) orless, unless otherwise specified.

In some embodiments, an article is presented. The article includes asubstrate and a thermal barrier coating disposed on the substrate. Thethermal barrier coating includes a plurality of aluminum-based particlesdispersed in an inorganic binder. The aluminum-based particles aresubstantially spaced apart from each other via the binder such that thethermal barrier coating is substantially electrically and thermallyinsulating.

FIG. 1 illustrates an article 100 in accordance with an embodiment ofthe disclosure. The article 100 includes a substrate 110 and a thermalbarrier coating 120 disposed on the substrate. As used herein, the term“thermal barrier coating” refers to a coating that includes a materialcapable of reducing heat flow to the underlying substrate of thearticle, that is, forms a thermal barrier. The term “thermal barriercoating” and “coating” are used herein interchangeably.

The thermal barrier coating may be further characterized by itsthickness. The thickness of the thermal barrier coating may depend uponthe substrate or the component it is deposited on. In some embodiments,the thermal barrier coating has a thickness in a range from about 50microns to about 3000 microns. In some embodiments, the thermal barriercoating has a thickness in a range of from about 25 microns to about1500 microns. In some embodiments, the thermal barrier coating has athickness in a range of from about 25 microns to about 1000 microns. Thethermal barrier coating may be disposed over a portion or over all ofthe substrate. The substrate may depend on the nature of the componenton which the thermal barrier coating is being applied. In someembodiments, the substrate includes a metal, a metal alloy, or acombination thereof. In certain embodiments, the substrate include iron,an iron alloy, aluminum, an aluminum alloy, or combinations thereof.

As used herein, the term “aluminum-based particles” refers to particlesincluding aluminum metal, alumina, an aluminum alloy, or combinationsthereof. Alumina typically has the formula Al₂O₃, and in the context ofthe present disclosure includes unhydrated and hydrated forms. As usedherein, the term “particles” refers to a particle, powder, flake, plate,rod, fiber, wire, mesh, or combinations thereof. The particles may beformed by, for example, grinding, shredding, fragmenting, pulverizing,atomization (for example, gas atomization), or otherwise subdividing alarger form of the material into a relatively small form. Thealuminum-based particles can be used in a variety of standard sizes. Thesize of the aluminum-based particles may depend on several factors, suchas the type of substrate; the technique by which the coating is to beapplied to the substrate; the identity of the other components presentin the coating; and the relative amounts of those components. Usually,the aluminum-based particles have an average particle size in the rangefrom about 0.5 microns to about 100 microns. In some embodiments, thealuminum-based particles have an average particle size in the range offrom about 0.5 microns to about 80 microns, from about 1 micron to about50 microns, from about 1 micron to about 30 microns, or any combination,sub-combination, range, or sub-range thereof.

In some embodiments, the plurality of aluminum-based particles issubstantially free of an aluminide. The term “aluminide” or“aluminide-containing” as used herein is meant to include a variety ofaluminum-containing materials that are typically used in coating metalalloys (especially superalloys), or which are formed during or after thecoating process (e.g., by diffusion process). Non-limiting examplesinclude platinum aluminide, nickel aluminide, platinum-nickel aluminide,refractory-doped aluminides, or alloys which contain one or more ofthose compounds. In certain embodiments, the plurality ofaluminum-particles includes less than 0.5 wt. % of an aluminide.

In certain embodiments, a surface region of the substrate issubstantially free of an aluminide. In certain embodiments, a surfaceregion of the substrate is substantially free of an aluminide formed bydiffusion of aluminum from the aluminum-based particles into thesubstrate. As used herein, the “surface region” usually extends to adepth of up to about 200 microns into the surface, and more frequently,to a depth of up to about 75 microns into the surface. This is incontrast to aluminum-based diffusion coatings as described earlier. Intypically diffusion coatings, the coating is subjected to heat treatmenttemperatures greater than 870° C., thereby diffusing the aluminum intothe surface region of the substrate and forming a metal aluminide. Thethermal barrier coatings of the present disclosure are substantiallyfree of the aluminide as the coatings are cured at temperatures lowerthan the diffusion temperature for aluminum into the substrate.

As used herein, the term “inorganic binder” refers to a composition,that, when cured, forms an amorphous, glassy matrix in which thealuminum-based particles are embedded in, are encapsulated in, areenclosed by, or otherwise adhered to. In some embodiments, the inorganicbinder includes a chromate, a phosphate, a molybdate, a vanadate, atungstate, or combinations thereof.

In embodiments, wherein the inorganic binder includes a chromate, thechromate is present as a hexavalent chromium in solution. Whiledescribing this form of chromium as chromate, it is to be understoodthat under acid conditions, the ion may be typically present as adichromate. The term “chromate” is used herein for convenience. Thechromate in solution may be supplied by chromic acid, by a metalchromate, or a dichromate. Chromate-containing inorganic bindercompositions can include one or more metal chromates, including aluminumchromates, magnesium chromates, zinc chromates, iron chromates, lithiumchromates, calcium chromates, or combinations thereof.

In embodiments, wherein the inorganic binder includes a phosphate, thephosphate is present as a phosphate ion in solution. The phosphate ioncan be supplied from a variety of sources including phosphoric acidsolutions and other materials such as phosphate salts of metalsincluding monobasic, dibasic and tribasic salts. Phosphate-containingbinder compositions can include one or more metal phosphates, includingaluminum phosphates, magnesium phosphates, chromium phosphates, zincphosphates, iron phosphates, lithium phosphates, calcium phosphates, orcombinations thereof. These salts can be used in conjunction withphosphoric acid to produce acid phosphate solutions. Other anhydrides orcompounds that produce phosphate in solution can be used such asphosphorous pentoxide, metaphosphorous acid, phosphorous acid andhypophosphorous acid. Phosphorous acid and hypophosphorous acid producephosphate ion in these binders by reaction with oxidizing agents such ashexavalent chromium in solution.

In embodiments, wherein the inorganic binder includes a molybdate, themolybdate is present as a molybdate ion in solution. The molybdate ioncan be supplied from molybdenum trioxide or metallic molybdates.

In certain embodiments, the inorganic binder includes a chromate and oneor more of a phosphate, a molybdate, a vanadate, and a tungstate. Insome such embodiments, the ratio of chromate to another binder (e.g.,phosphate) may vary in a range of from about 1:4 to about 4:1 by weight.In certain embodiments, the inorganic binder includes achromate-phosphate binder.

Because of the toxicity and potential carcinogenic properties ofhexavalent chromium, special handling procedures may need to betypically employed, in order to satisfy health and safety regulations.The special handling procedures can often result in increased costs anddecreased productivity. Therefore, in certain other embodiments, theinorganic binder is substantially free of hexavalent chromium. In somesuch embodiments, the inorganic binder includes colloidal silica. Theterm “colloidal silica” as used herein refers to particles of silica.Dispersions of colloidal silica are available from various chemicalmanufacturers, in either acidic or basic form. Moreover, various shapesof silica particles may be used, e.g., spherical, hollow, porous, rod,plate, flake, or fibrous, as well as amorphous silica powder.

As will be appreciated by one of ordinary skill in the art, thealuminum-based particles and the binder compositions (such as, forexample, chromate, phosphate, or colloidal silica) may further interactor react with each other during one or more of disposing andpost-processing steps. Therefore, the terms “aluminum-based particles”and “inorganic binder” as used herein connotate both the non-reacted aswell as reacted forms of the particles and the binder.

The composition of the thermal barrier coating in terms of the amount ofthe aluminum and the inorganic binder may depend upon one or morefactors, including the composition of the adjacent bond coat layer (ifpresent), the coefficient of thermal expansion (CTE) characteristicsdesired for the thermal barrier coating, and the thermal barrierproperties desired for the thermal barrier coating. In certainembodiments, the amount of aluminum-based particles (sometimes referredto in the art as “aluminum loading”) may be maintained in the thermalbarrier coating such that the thermal barrier coating is substantiallythermally and electrically insulating. This is in contrast tosacrificial corrosion resistant coatings employed for metallicsubstrates, as discussed herein earlier. Although, these aforementionedsacrificial corrosion resistant coatings may also include aluminum-basedparticles in an inorganic binder, the aluminum loading of these coatingsis maintained such that these corrosion resistant coatings aresubstantially electrically conductive.

As used herein, the term “substantially electrically insulating” meansthat the thermal barrier coating has an electrical resistivity greaterthan 1 ohm·metre (Ω·m). In some embodiments, the electrical resistivityof the thermal barrier coating is greater than 10² am. As used herein,the term “substantially thermally insulating” means that the thermalbarrier coating has a thermal conductivity lower than 2.2 W/m-K. In someembodiments, the thermal conductivity of the thermal barrier coating islower than 1.5 W/m-K.

In some embodiments, the plurality of aluminum-based particles ispresent in the thermal barrier coating in an amount in a range fromabout 20 volume percent to about 70 volume percent, in a range fromabout 30 volume percent to about 60 volume percent, in a range fromabout 50 volume percent to about 60 volume percent, or any combination,sub-combination, range, or sub-range thereof; and the binder is presentin the thermal barrier coating in an amount in a range from about 30volume percent to about 80 volume percent, in a range from about 40volume percent to about 70 volume percent, in a range from about 40volume percent to about 50 volume percent or any combination,sub-combination, range, or sub-range thereof. In certain embodiments,the plurality of aluminum-based particles is present in the thermalbarrier coating in an amount in a range from about 40 volume percent toabout 50 volume percent and the binder is present in the thermal barriercoating in an amount in a range from about 50 volume percent to about 60volume percent. As mentioned previously, the loading of aluminum in thethermal barrier coating is controlled such that the thermal barriercoating is substantially electrically insulating.

The thermal barrier coating is further characterized by the averagedomain size of the aluminum-based particles and the inorganic binder.This is further illustrated in FIG. 2, wherein an expanded portion of athermal barrier coating 120 is illustrated. The thermal barrier coatingincludes the plurality of aluminum-based particles 130 dispersed in theinorganic binder 140. The plurality of aluminum-based particles 130 isfurther characterized by a domain size 13 and the inorganic binder ischaracterized by a domain size 14.

An average domain size of the aluminum-based particles in the thermalbarrier coating may be least 0.5 microns, at least 1 micron, at least 2microns, in a range from about 0.5 microns to about 30 microns, in arange from about 1 micron to about 10 microns, or any combination,sub-combination, range, or sub-range thereof. Similarly, an averagedomain size of the binder in the thermal barrier coating may be at least0.5 microns, at least 1 micron, at least 2 microns, in a range fromabout 0.5 microns to about 5 microns, in a range from about 1 micron toabout 5 microns, or any combination, sub-combination, range, orsub-range thereof.

In certain embodiments, the aluminum-based particles dispersed in theinorganic matrix may be further characterized by a core-shell structure.FIG. 3 illustrates a schematic of a thermal barrier coating including120 including a plurality of aluminum-based particles 130 having acore-shell structure, for example. In the embodiment illustrated in FIG.3, the particle 130 includes a core 132 and a shell 134. It should benoted, that for the purposes of illustration, the aluminum-basedparticles in FIGS. 1 and 3 are depicted as having a spherical shape,however, other shapes of the aluminum-based particles are alsoencompassed within the scope of the disclosure. For example, thealuminum-based particles may have a conical, tubular, square,rectangular, or any other irregular shape.

In certain embodiments, the core 132 of the core-shell structureincludes aluminum metal and the shell 134 of the core-shell structureincludes a complex of the binder and one or both of aluminum andalumina. The term complex as used herein includes both covalently andnon-covalently bound compounds of the binder with the aluminum/alumina.In certain embodiments, wherein the binder includes a chromate-phosphatebinder, the core 132 of the core-shell structure includes aluminum metaland the shell 134 of the core-shell structure includes at least one ofan aluminum chromate phosphate and an alumina chromate phosphate. Insome such embodiments, as illustrated in FIG. 4, the shell 134 of thecore-shell structure may further include a first layer 135 disposedproximate to the core 132 and a second layer 136 disposed on the firstlayer 135. In some such instances, the first layer 135 includes aluminumchromate phosphate and the second layer 136 includes alumina chromatephosphate.

The core 132 of the core-shell structure may have an average size of atleast 0.5 microns, at least 1 micron, at least 2 microns, in a rangefrom about 0.5 microns to about 30 microns, in a range from about 1micron to about 10 microns, or any combination, sub-combination, range,or sub-range thereof. The term “size” as used in this context refers tothe largest dimension of the core 132 in the core-shell structure, andas will apparent to one of ordinary skill in the art will depend on theshape of the core-shell structure. Similarly, a thickness of the shell134 of the core-shell structure may be at least 0.5 microns, at least 1micron, at least 2 microns, in a range from about 0.5 microns to about 5microns, in a range from about 1 micron to about 5 microns, or anycombination, sub-combination, range, or sub-range thereof. Further,although the thickness of the shell 134 is illustrated as substantiallyuniform in FIG. 4, the thickness may be non-uniform and vary around theperiphery of the core 132.

In some embodiments, the article may further include a bond coatingdisposed between the substrate and the thermal barrier coating. FIG. 5illustrates an embodiment wherein the article 100 includes a bondcoating 150. In the embodiment illustrated in FIG. 5, the article 100includes a bond coating 150, a thermal barrier coating 120, and aprotective coating (also referred to as top-coat) 160. The bond coating150 may be formed from a metallic oxidation-resistant material thatprotects the underlying substrate and enables the thermal barriercoating to more tenaciously adhere to substrate. The bond coating 150may have a thickness in the range of from about 25 microns to about 500microns. In some embodiments, the protective coating 160 may include aCMAS-reactive protective coating, an environmental barrier coating, oran erosion resistant layer.

The coatings of the present disclosure may be useful in a wide varietyof components that are operated at, or exposed to, high temperatures. Incertain embodiments, the article includes an automotive component, alocomotive component, a marine component, or a medical component. Insome such embodiments, the article includes a diesel engine component.In certain embodiment, automotive components including the thermalbarrier coatings in accordance with embodiments of the disclosure arealso presented. Non-limiting examples of automotive components include apiston, a valve, a cylinder head, an exhaust pipe, a turbo housing, acatalyst container, an exhaust manifold, or combinations thereof. Incertain embodiments, the thermal barrier coatings of the presentdisclosure are particularly useful for providing thermal protection topistons in an automotive engine. In some such embodiments, the substrateincludes aluminum, iron, or a combination thereof.

In some embodiments, a method of forming a thermal barrier coating on asubstrate is also presented. The thermal barrier coating may be disposedor otherwise formed on a bond coating (if present) or on the substratedirectly by any of a variety of conventional techniques. The particulartechnique used for disposing, depositing or otherwise forming thethermal barrier coating may depend on one or more of the composition ofthe thermal barrier coating, the thickness, and the physical structuredesired for the thermal barrier coating. In certain embodiments, thethermal barrier coating is disposed on a bond coating (if present) or onthe substrate directly, using a slurry.

Referring now to FIGS. 6 and 7, a method 1000 of forming a thermalbarrier coating 120 on a substrate 110 is illustrated. The methodincludes, at step 1001, contacting a slurry including a plurality ofaluminum-based particles and an inorganic binder with a surface 101 ofthe substrate 110 to form a slurry coating 121. Suitable examples of theplurality of aluminum-based particles and the inorganic binder have beendescribed herein earlier.

Use of a slurry for disposing a thermal barrier coating may present manyadvantages. For example, slurries can be easily and economicallyprepared, and their aluminum content can be readily adjusted to meet therequirements for a particular substrate. Moreover, the slurries can beapplied to the substrate by a number of different techniques, and theirwetting ability helps to ensure relatively uniform thickness. The slurryincludes a plurality of aluminum-based particles and an organic binder,typically suspended or otherwise contained in a liquid carriercomponent. As used herein, the term “liquid carrier component” refers toany carrier component that is liquid at ambient temperatures and inwhich the aluminum-based particles and an organic binder is typicallycarried in, dispersed in, dissolved in, etc. Liquid carrier componentsinclude aqueous systems (e.g., including water), organic systems (e.g.,including alcohols such as ethanol, propanol, isopropanol, etc., otherliquid organic materials or solvents such as ethylene glycol, acetone,toluene, xylene, alkanes, etc.) or any combination thereof. These liquidcarrier components can include other optional materials such assurfactants, buffers, etc. Aqueous carrier component can consistessentially of water, i.e., is substantially free of other optionalmaterials, but more typically includes other optional materials such ascompatible organic solvents, surfactants, etc. Suitable surfactants foruse in aqueous carrier components can include nonionic surfactants,anionic surfactants, cationic surfactants, amphoteric surfactants,zwitterionic surfactants, or any combination thereof.

The slurry can be loaded with a varying proportion of aluminum-basedparticles and the inorganic binder, depending upon the desiredrheological properties of the slurry, coating thickness, or desiredloading of the aluminum-based particles in the thermal barrier coating.In some embodiments, the amount of liquid carrier solvent in the slurryis in an amount in a range from about 10 volume percent to about 50volume percent, in a range from about 20 volume percent to about 40volume percent, in a range from about 25 volume percent to about 30volume percent, or any combination, sub-combination, range, or sub-rangethereof. In some embodiments, the volume ratio of aluminum-basedparticles to the inorganic binder in the slurry is in an amount in arange from about 0.5 to about 1.2, in a range from about 0.5 to about 1,in a range from about 0.67 to about 1, or any combination,sub-combination, range, or sub-range thereof. The slurry may furtherinclude other optional components such as colorants or pigments,viscosity modifying or controlling agents, etc.

Referring again to FIGS. 6 and 7, the method 1000 according toembodiments of the present disclosure includes a step 1001 of contactinga slurry with at least a portion of a surface 101 of the substrate 110.Some embodiments include a step 1001 of contacting the slurry withsubstantially all of a surface 101 of the substrate 110. The slurry canbe contacted with the substrate by a variety of techniques known in theart. In some embodiments, the slurries can be slip-cast, brush-painted,dipped, sprayed, poured, rolled, or spun-coated onto the substratesurface, for example. In certain embodiments, the slurry is spray-coatedon a surface of the substrate. The viscosity of the coating can bereadily adjusted for spraying, by varying the amount of the liquidcarrier used.

The slurry can be applied as a single layer or multiple layers.Therefore, in some embodiments, the step 1001 may be effected multipletimes until a desired thickness of the slurry coating 121 is achieved.In some embodiments, the slurry coating 121 has a thickness in a rangefrom about 50 microns to about 3000 microns. In some embodiments, theslurry coating has a thickness in a range of from about 25 microns toabout 1500 microns. In some embodiments, the slurry coating has athickness in a range of from about 25 microns to about 1000 microns.

Referring again to FIGS. 6 and 7, the method further includes, at step1002, heat-treating the slurry coating 121 under conditions sufficientto cure the slurry coating 121 and form the thermal barrier coating 120.As noted earlier, the formed thermal barrier coating 120 coatingincludes aluminum-based particles that are substantially spaced apartfrom each other via the binder in the thermal barrier coating such thatthe thermal barrier coating is substantially electrically and thermallyinsulating.

In some embodiments, after an initial application of the slurry to thesubstrate surface, the slurry coating may be dried to substantiallyremove any volatiles. After the full thickness of the slurry coating hasbeen applied, an additional, optional heat treatment (drying step) maybe carried out, to further remove volatile materials like additionalsolvents (if used) and water. The heat treatment conditions for dryingwill depend in part on the identity of the volatile components in theslurry. In some embodiments, this drying step may include, for example,air drying for a period (e.g., greater than 15 minutes) and at atemperature (e.g., from about 70° C. to a about 100° C.). If a series oflayers is used, a drying step can be performed after each layer isdeposited, to accelerate removal of the volatile components.

After drying, the slurry coating 121 may be cured using suitable heattreatment conditions to form the thermal barrier coating, at step 1002,as shown in FIGS. 6 and 7. As used herein, the term “curing” refers toany treatment condition or combination of treatment conditions thatcauses the slurry coating to form the thermal barrier coating. Adiscussed previously, in certain embodiments, the slurry coating isheat-treated at a temperature lower than a temperature sufficient fordiffusing aluminum from the aluminum-based particles into a surfaceregion of the substrate. In some embodiments, the slurry coating isheat-treated at a temperature lower than 300° C., at a temperature lowerthan 250° C., at a temperature in a range from about 150° C. to about250° C., at a temperature in a range from about 170° C. to about 200°C., or any combination, sub-combination, range, or sub-range thereof.

If more than one contacting step 1001 is employed, then drying and/orcuring may be conducted after each contacting step 1001. In someembodiments. the method may further include subjecting the cured slurrycoating to a burnishing step to form the thermal barrier coating.

The thermal barrier coating may be formed off-site or on-site, to in-usecomponents, to new components, or a combination thereof. As used herein,in-use component refers to any component which has been previouslymanufactured for and/or placed in operation. If necessary or desired,(as in for example, a repair method), the article (e.g., a diesel enginecomponent) may be mechanically worked prior to application of theslurry, for example, to remove damage or to smooth the surface of theengine component.

Without being bound by any theory, it is believed that the thermalbarrier coatings of the present disclosure may provide the requiredthermal barrier properties in a cost-effective manner as an alternativeto ceramic thermal barrier coatings. In particular, inventors of thepresent disclosure have found that the thermal barrier coatingsincluding aluminum-based particles in an inorganic binder provide thedesired thermal barrier coating properties for automotive components,such as, pistons in a cost-effective manner.

Examples

An internal combustion engine was coated with a slurry compositionincluding aluminum particles and a chromate-phosphate binder. Portionsof the pistons were subjected to sequential surface preparation, spraycoating and burnishing steps to form a thermal barrier coating having athickness of about 150±15 microns. Mechanical properties (e.g.,hardness), thermal conductivity, coefficient of thermal expansion match,durability (e.g., spallation) and microstructure of the coatings wereevaluated. The thermal barrier coatings exhibited the desired thermalconductivity and coefficient of thermal expansion match with thesubstrate. Further, the thermal barrier coatings after standard enginetest procedure exhibited no or minimal spallation, and superior hardnessvalues. Optical micrographs of the microstructure (as shown in FIG. 8)showed distinct plurality of aluminum particulate domains(aluminum-based particles 130) dispersed in the binder 140 matrix.

The foregoing examples are merely illustrative, serving to exemplifyonly some of the features of the invention. The appended claims areintended to claim the invention as broadly as it has been conceived andthe examples herein presented are illustrative of selected embodimentsfrom a manifold of all possible embodiments. Accordingly, it is theApplicants' intention that the appended claims are not to be limited bythe choice of examples utilized to illustrate features of the presentinvention. As used in the claims, the word “comprises” and itsgrammatical variants logically also subtend and include phrases ofvarying and differing extent such as for example, but not limitedthereto, “consisting essentially of” and “consisting of” Wherenecessary, ranges have been supplied; those ranges are inclusive of allsub-ranges there between. It is to be expected that variations in theseranges will suggest themselves to a practitioner having ordinary skillin the art and where not already dedicated to the public, thosevariations should where possible be construed to be covered by theappended claims. It is also anticipated that advances in science andtechnology will make equivalents and substitutions possible that are notnow contemplated by reason of the imprecision of language and thesevariations should also be construed where possible to be covered by theappended claims.

1. An article, comprising: a substrate; and a thermal barrier coatingdisposed on the substrate, wherein the thermal barrier coating comprisesa plurality of aluminum-based particles dispersed in an inorganicbinder, wherein the aluminum-based particles are substantially spacedapart from each other via the inorganic binder such that the thermalbarrier coating is substantially electrically and thermally insulatingand the aluminum-based particles comprise aluminum metal, an aluminumalloy or combinations thereof. 2-9. (canceled)
 10. The article of claim1, wherein the article comprises an automotive component, a locomotivecomponent, a marine component, or a medical component. 11-14. (canceled)15. A method of forming a thermal barrier coating on a substrate, themethod comprising (i) contacting a slurry comprising a plurality ofaluminum-based particles and an inorganic binder with a surface of thesubstrate to form a slurry coating; and (ii) heat-treating the slurrycoating under conditions sufficient to cure the slurry coating and formthe thermal barrier coating, wherein the aluminum-based particles aresubstantially spaced apart from each other via the inorganic binder inthe thermal barrier coating such that the thermal barrier coating issubstantially electrically and thermally insulating, and wherein thealuminum-based particles comprise aluminum metal, an aluminum alloy orcombinations thereof.
 16. The method of claim 15, wherein a volume ratioof the aluminum-based particles to the inorganic binder in the slurry isin a range from about 0.67 to about
 1. 17. The method of claim 15,wherein the slurry coating is heat-treated at a temperature lower than atemperature sufficient for diffusing aluminum from the plurality ofaluminum-based particles into a surface region of the substrate.
 18. Themethod of claim 17, wherein the slurry coating is heat-treated at atemperature lower than 300° C.
 19. (canceled)
 20. The method of claim15, wherein the inorganic binder comprises a chromate, a phosphate, amolybdate, a vanadate, a tungstate, or combinations thereof.
 21. Themethod of claim 15, wherein the inorganic binder is substantially freeof hexavalent chromium.
 22. The method of claim 15, wherein an averagedomain size of the plurality of aluminum-based particles in the curedslurry coating is in a range from about 0.5 microns to about 30 microns.23. The method of claim 15, wherein an average domain size of theinorganic binder in the cured slurry coating is in a range from about0.5 microns to about 5 microns.
 24. The method of claim 15, wherein theplurality of aluminum-based particles is present in the cured slurrycoating in an amount in a range from about 20 volume percent to about 70volume percent, and the inorganic binder is present in the cured slurrycoating in an amount in a range from about 30 volume percent to about 80volume percent.
 25. The method of claim 15, wherein the inorganic bindercomprises a chromate, a phosphate, a molybdate, a vanadate, a tungstate,or combinations thereof.
 26. The method of claim 15, wherein theplurality of aluminum-based particles comprises a core-shell structure.27. The method of claim 26, wherein a core of the core-shell structurecomprises aluminum metal and a shell of the core-shell structurecomprises a complex of the inorganic binder and aluminum.
 28. The methodof claim 15 further comprising burnishing the cured slurry.
 29. Themethod of claim 15, wherein the cured slurry coating has an electricalresistivity greater than 1 ohm·m and a thermal conductivity lower than2.2 W/m-K.
 30. The method of claim 15 further comprising disposing abond coating between the substrate and the thermal barrier coating.